(1) Field Of The Invention
The present invention relates to a surface-modified plastic plate for use in optical disc bases to make the bases free of misreading due to pitting, windows of aircraft for windproofing, windows of automobiles or of architectural structures, solar cell receptors, liquid crystal display panels, protective sheets for computer touch panels, etc.; the surface modified plastic plate is lightweight and shows improvements in mar-proof properties, impact resistance, prevention of adhesion of dust due to electrification and in weather resistance.
(2) Description Of The Prior Art
The optical disc as the high density recording medium has been practically used not only as one to be exclusively used for regeneration, but also as ones to be used for postscript, rewriting, etc., that is, various kinds of optical discs have been practically used. At present, plastics such as polymethyl methacrylate polymer, polycarbonate and the like, are used as an optical disc base material. Since these plastics have high static electrification properties and unsatisfactory hardness, adhesion of dust onto the surface and development of marrings on the surface take place, often resulting in errors on reading. When the optical disc is used, the spill of an alcoholic drink thereonto also creates problems such as whitening. For the purpose of solving the above problems, a method of forming an acrylate based protective film layer onto an optical disc base, a method of incorporating an antistatic agent for destaticizing, etc., have been developed. These methods, however, raise problems so that it is impossible for them to obtain satisfactory mar resistance and antistatic properties, and in addition, the incorporation of the antistatic agent results in a further reduction in solvent resistance.
A plastic plate which comprises polymethyl methacrylate or the like, which is light in weight and has good transparency, has been used in the art as a window in aircraft for wind-proofing. However, use of the above plastic plate itself raises a problem whereby crazing develops on the surface in a service time of about 2 years, resulting in a loss of clarity.
Reasons for the development of crazing may include physical factors and chemical factors. The physical factor may include marring of the surface of the plastic plate due to the action of dust which develops micro-cracking followed by enlargement of the micro-cracking to develop macro-cracking, etc. The chemical factor may include etching of the surface of the plastic plate by acid rain, etc.
In order to prevent development of the above crazing, there has been proposed a process for preventing the development of crazing which comprises forming a film selected from an organic film which comprises, for example, polyester-urethane, polyurethane, methacrylate polymer or the like, and from an inorganic film which comprises, for example, tin oxide, indium oxide or the like onto a plastic substrate. However, the process which comprises the formation of the organic film raises such problems as the film being incapable of obtaining satisfactory hardness, chemical resistance and antistatic properties. On the other hand, the process which comprises the formation of the inorganic film raises such problems as the film being incapable of obtaining a satisfactory adhesion to the plastic substrate.
In recent years, studies have been made on how to make cars more lightweight for the purposes of reduction in fuel consumption and improvement of running performance. A sandwich panel formed by sandwiching a resin between glasses is generally known as the window for use in automobiles. Since the sandwich panel, however, is heavy, replacement of glass by plastic is being carried out as a means of decreasing automobile weight.
On the other hand, the windows used in architectural structures are generally made of glass and raise problems such as how easily they can be broken by impact. Particularly, windows unbreakable by impact are demanded and replacement of glass by plastic is being carried out in the case of large-sized windows, windows used in a terrace as a shelter against rain, windows used in high-rise buildings, etc. because of the frequency of glass cracking, the safety involved, cost of repairing, etc.
The transparent, lightweight plastic substrate is widely used as a substitute for window glass for use in building materials, automobiles and architectural structures because of its high mechanical strength and impact resistance as well as ease of fabrication. On the other hand, use of the above plastic substrate raises problems such as the surface of the plastic plate being more easily marred and more easily whitened by marring, such as dust more easily adhering onto the surface of the plastic plate due to electrification, and further that yellowing may more easily take place when the plastic plate is used outdoors as compared with glass.
Recently, the solar cell has widely been used as a part of energy saving. A protective plate used in the receptor of the solar cell and corresponding to a window therein is formed by use of a plastic plate, and raises problems such as its energy conversion efficiency being reduced because of yellowing due to exposure to sun light, development of marrings and adhesion of dust.
A protective plate used in a liquid crystal display panel of a liquid crystal display and corresponding to a window therein is being replaced by a lightweight plastic plate in place of a glass plate, which results in problems such as the development of marrings on the surface, adhesion of dust onto the surface due to electrification, and the like.
A plastic plate such as a polycarbonate plate or the like has been used as a protective sheet of a touch panel of a computer, etc., which results in problems such as the development of marrings caused by touching the surface with one's fingers, pollution caused by adhesion of dust on the surface of a display section, and the like.
Thus, improvements of the above-mentioned plastic plates for use in the windows of aircraft, automobiles, architectural structures, solar cell receptors, liquid crystal display panels, protective sheets of computer touch panels, etc. are demanded; for example, improved hardness properties, anti-marring properties, antistatic properties, chemical resistance and improved weather resistance.
For the purpose of solving the above problems, there is proposed a process which comprises forming a film by means of a physical deposition of silica, etc. on the surface of a plastic plate to cover the surface of the plastic plate with a ceramic film. However, the process results in raising such problems as unsatisfactory adhesion properties between the plastic plate and the ceramic film which makes the adhesion easily separated under high temperatures and high humidity.